The present invention relates to a composite shaped article of a vinyl chloride-based resin clad with a coating layer of a polyvinyl alcohol and a method for the preparation thereof.
Needless to say, vinyl chloride-based resins belong to one of the most important classes of thermoplastic resins owing to their very unique and versatile properties if not to mention their remarkable inexpensiveness in comparison with other thermoplastic resins. They have, however, some defective points presenting a drawback in their wider applications. For example, films of a polyvinyl chloride resin have relatively large gas permeability so that their use is not recommended when absolute shielding of gas permeation is essential.
Further, surfaces of shaped articles of a polyvinyl chloride resin are readily charged up with static electricity inducing deposition of dusts from the ambient environment to a loss of the surface beautifulness. Moreover, surfaces of shaped articles of vinyl chloride-based resins are sometimes not satisfactory with respect to the mechanical strengths, e.g. resistance against scratch, and resistance against chemicals. Therefore, it has been one of the important problems to improve surface properties of a shaped article of vinyl chloride-based resins in these respects.
Among several attempts hitherto made for solving the above problems, it is one of promising approaches that a shaped article of a vinyl chloride resin is clad or provided with a coating film of another kind of resin such as polyethylene, polypropylene, polyesters and the like by use of a suitable adhesive agent such as polyurethane-based ones. If setting aside the problem that curved or irregular surfaces are bonded with plain films of overcoating hardly or with extreme difficulty, this method is effective provided that the kind of the overcoating resin is properly selected and strong adhesive bonding is obtained between the overcoating resin and the polyvinyl chloride resin.
As a matter of course, a single kind of the overcoating resin cannot be a remedy for all defective properties desired to be improved of the vinyl chloride-based resin since an overcoating resin has its own defective points. Therefore it is a usual practice to select the overcoating resin in accordance with one or a few specific properties to be improved depending on the intended application of the shaped article. Accordingly, in these circumstances, it is sometimes desired that a shaped article of a vinyl chloride-based resin is clad with a polyvinyl alcohol so as to be able to utilize the unique properties inherently possessed by polyvinyl alcohols. Unfortunately, such a polyvinyl alcohol-clad shaped article of a vinyl chloride-based resin has not yet come to practical use due to the technical difficulties to obtain strong bonding between the surface of a polyvinyl chloride shaped article and a film of polyvinyl alcohol such as the absence of a suitable adhesive agent.